Just curious! My 30 will hold the 10th round in the mag, but it seems to be almost an unnatural fit, meaning I really have to fight to squeeze the round in! And, with a round chambered, the gun will not accept a a full 10 round mag. Works fine with 9+1, but not 10+1! Anyone have this problem? And if this is common why does Glock advertise and promote 10+1 for the Glock30??

I do not own a Glock 30 but have encountered this situation and its the magazine not the gun. If you load 10 in the mag and chamber a round and then replace the 10 round and put it back in the gun it will probably work fine.

I understand the mag springs might be tight! But why will the gun not accept 10 round mags with 1 in the chamber is my bigger concern/question?

It will. Unless defective which is unlikely. The G30 is my HD, and I competed with it. It could take a Krav Maga strike to send the mag home. But also make sure the top round is seated all the way to the back.

It is not recommended to load one in the chamber plus remove the mag and add one back. The magazines, regardless of make, are designed to be loaded with an open slide when at the full capacity. When you remove the mag and add one back or try to insert a fully loaded mag with a closed slide, the spring is often compressed beyond where it should. Worse yet, the cartridge may tilt in such a manner as to prevent feeding of the round (very bad if this is your carry gun and you get an FTF). There are exceptions, such as a 7 rd. 1911 magazine, which has enough room for the compressed spring coils. Not so with a 1911 8 round flush fit mag. Same with the Glock, although a double stack Glock mag is sometimes more forgiving. Regardless, is one more round really more important than reliable feeding?